The Nervous System and Neuronal Excitability

Flashcards covering key vocabulary terms related to the nervous system and neuronal excitability, including electrical signals, action potential phases, synaptic transmission, neurotransmitters, and neural circuits.

Graded Potentials

Electrical signals generated along the membrane of dendrites and cell bodies, signaling over short distances.

Action Potentials

Electrical signals initiated at the axon hillock and generated along the membrane of axons, signaling over long distances.

Depolarizing Graded Potential

A small deviation from resting membrane potential that makes the membrane potential less polarized.

Hyperpolarizing Graded Potential

A small deviation from resting membrane potential that makes the membrane potential more polarized.

Graded Potential Amplitude

Can vary in size depending on the strength of the stimulus.

Summation of Graded Potentials

When two or more graded potentials add together.

Decremental Conduction

The amplitude of a graded potential decreases with distance from the initial site.

Action Potential (AP)

A rapid reversal of the membrane potential due to changes in membrane permeability to Na+ and K+.

Non-decremental Propagation

Action potentials travel the length of an axon without decreasing in amplitude.

All-or-None Event

Once threshold has been reached, an action potential will occur, independent of stimulus strength.

Threshold Potential

The critical level of depolarization the cell membrane must reach to trigger an action potential.

Depolarization Phase (AP)

The rapid rising phase of the action potential due to a positive feedback cycle causing voltage-gated Na+ channels to open, making the cell momentarily positive.

Repolarization Phase (AP)

The phase where Na+ channels are inactivated and voltage-gated K+ channels open, causing the membrane potential to fall back towards rest.

Voltage-gated Na+ Channels

Ion channels that exist in closed (capable of opening), open (activated), and closed (inactivated) conformations, crucial for the depolarizing phase of an AP.

Voltage-gated K+ Channels

Ion channels that are slower to open than Na+ channels and do not have inactivation gates, contributing to the repolarizing phase of an AP.

Action Potential Frequency

How the nervous system codes for stimulus strength, with stronger stimuli causing a higher rate of action potentials.

Subthreshold Stimulus

A stimulus not strong enough to depolarize the membrane to the threshold potential.

Suprathreshold Stimulus

A stimulus stronger than necessary to depolarize the membrane to the threshold potential, still producing an all-or-none action potential.

After-hyperpolarizing Phase (AP)

The undershoot observed after the resting membrane potential is reestablished, typically going down to -90mV.

Refractory Period

A period during which an action potential cannot be generated or requires a stronger stimulus, limiting the frequency of APs.

Absolute Refractory Period

A period when Na+ channels are inactivated and cannot be opened, making it impossible to generate another action potential.

Relative Refractory Period

A period when K+ channels are still open, requiring a stronger than normal stimulus to generate an action potential.

One-way Conduction

The property of action potentials due to the refractory period, ensuring signal propagation in a single direction down the axon.

Axon Hillock

The region of a neuron where action potentials are typically initiated.

Continuous Conduction

Conduction in unmyelinated neurons where action potentials are produced down the entire length of the axon at every patch of membrane, resulting in slower propagation.

Saltatory Conduction

Conduction in myelinated neurons where action potentials 'leap' between concentrated Na+ ion channels at the Nodes of Ranvier, greatly increasing conduction speed.

Action Potential Conduction Speed

Determined by the diameter of the axon and the degree of myelination.

Synapse

The functional connection between a neuron and the cell it is signaling, or the point at which one neuron communicates with another neuron or a target tissue.

Presynaptic Neuron

The neuron that sends the signal across a synapse.

Postsynaptic Neuron

The neuron that receives the signal at a synapse.

Synaptotagmin

A protein that serves as a Ca2+ sensor, binding calcium ions to initiate neurotransmitter release from synaptic vesicles.

SNARE Proteins

Proteins (Synaptobrevin, SNAP-25, Syntaxin) that dock synaptic vesicles at the plasma membrane, facilitating vesicle fusion and neurotransmitter release.

Neurotransmitter Termination

The process by which neurotransmitters are degraded or removed from the synapse to end signal transduction.

Inhibitory Post-Synaptic Potential (IPSP)

Neurotransmitter release that results in a hyperpolarization of the post-synaptic membrane, making it less likely to fire an action potential.

Excitatory Post-Synaptic Potential (EPSP)

Neurotransmitter release that results in a depolarization of the post-synaptic membrane, making it more likely to fire an action potential.

Summation of IPSP and EPSP

The algebraic summing of all excitatory and inhibitory postsynaptic potentials, which determines if an action potential will be generated.

Ionotropic Receptors

Neurotransmitter receptors that function directly as ligand-gated ion channels.

Metabotropic Receptors

Neurotransmitter receptors that function indirectly through a G-protein to produce a slower, more prolonged response.

Presynaptic Modulation

Regulation of neurotransmitter release from a presynaptic neuron by another neuron, leading to either increased (facilitation) or decreased (inhibition) release.

Acetylcholine (ACh)

A small-molecule neurotransmitter whose effect (EPSP or IPSP) depends on the specific receptor subtype.

Endocannabinoids

Neurotransmitters that bind to cannabinoid receptors, involved in pain processing and appetite stimulation; example: Anandamide.

Glutamate (Glu)

The most prevalent excitatory amino acid neurotransmitter in the brain.

Norepinephrine (NE) and Epinephrine (E)

Biogenic amine neurotransmitters that are part of the sympathetic nervous system.

Dopamine

A biogenic amine neurotransmitter important in reward pathways.

Serotonin

A neurotransmitter often referred to as the 'happy' neurotransmitter, targeted by SSRIs (selective serotonin reuptake inhibitors).

Opioid Peptides

Neuropeptides like enkephalins, endorphins, and dynorphins that bind to opioid receptors, acting as natural pain relievers.

Substance P

A neuropeptide that is part of the pain pathway.

Diverging Circuit

A neural circuit where a single presynaptic neuron synapses with several postsynaptic neurons, spreading the signal to multiple pathways.

Converging Circuit

A neural circuit where a postsynaptic neuron receives action potentials from several different sources, allowing for signal integration.

Reverberating Circuit

A neural circuit where branches from later neurons synapse with earlier ones, sending action potentials back through the circuit repeatedly.

Parallel After-discharge Circuit

A neural circuit where a single presynaptic cell stimulates a group of neurons, each synapsing with a common postsynaptic cell, allowing for prolonged output.

Curare

A toxin that acts as an antagonist of acetylcholine, blocking neuromuscular transmission.

Sarin

A nerve gas that inhibits acetylcholinesterase, leading to prolonged acetylcholine effects.

Botulinum Toxin (Botox)

A toxin that inhibits the release of acetylcholine (ACh), causing flaccid paralysis.

Tetrodotoxin

A potent toxin (e.g., from Puffer fish) that blocks voltage-gated Na+ channels, disrupting nerve impulse conduction.

Saxitoxin

A toxin associated with red tide algae that blocks voltage-gated Na+ channels.

α-Bungarotoxin

A venom from Bungarus snakes that binds to ACh receptor proteins and prevents ACh from binding.

Neostigmine

A drug that inhibits acetylcholinesterase in the postsynaptic membrane.

Strychnine

A toxin that prevents inhibitory postsynaptic potentials (IPSPs) in the spinal cord, causing uncontrolled muscle contraction.